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Estheticians perform treatments on the skin’s barrier every day; and although it is the last thing a skin therapist intends to do, they could be damaging the skin’s barrier unknowingly during treatment. Corneobiology can help us to better understand what is happening in skin by identifying the multiple actions that take place in the skin’s barrier. This body of science can be adopted through the skin therapy approach called corneotherapy. This article will take a closer look at corneotherapy and decipher how it can be applied to the treatment room.

What is Corneotherapy?

Corneotherapy refers to therapeutic interventions aimed at repairing stratum corneum barriers impaired through dermatologic disorders such as atopic dermatitis, psoriasis, irritant allergic contact dermatitis and chronic alipidic skin. This therapy is centered around the science of corneobiology, which is focused on the anatomy, physiology and biology of the stratum corneum. Corneobiology encompasses disciplines including immunology, endocrinology and psychology, all of which have a connection to the central nervous system.

Until the latter half of the 20th century, the stratum corneum was viewed as an impermeable barrier to the environment, with no biological function. This is when Albert Kligman, M.D., conducted a series of experiments showing that the stratum corneum is biologically active cellular tissue; this is also when the understanding of topical therapies changed. Kligman named these therapies corneotherapy. The study of corneobiology was further enhanced by the work of Peter Elias, M.D., who defined the fundamental functions of the stratum corneum. He outlined 10 functions of this horny layer, and collaborating with Kligman, added six more for a total of 16, explained next.

Functions of the Stratum Corneum

Permeability. Think hydration, essential lipid ratios and the pH of the acid mantle.

Antimicrobial. This also relates to the pH of the acid mantle and permeability barrier.

Antioxidant. Vitamin D production is an example of this.

Cohesion (integrity). Desquamation

Mechanical. The corneocyte envelopes and keratin filaments are related to this.

Chemical. This is focused on the exclusion of antigens.

Psychosensory.

Hydration. The permeability barrier and skin’s ability to hold water are the focus.

Protection against electromagnetic radiation.

Initiation of inflammation. (Through cytokine activation)

Biosensor of meteorological conditions. This is especially relative to humidity.

Regulator of innate and adaptive immunity.

Storage site for topical drugs, cosmetics and cosmeceuticals. Be careful with sensitive skin ingredients such as lactic acid, as this can be stored and washing will not remove it.

Protection against carcinogens and photoaging.

Organ of social communication.

Generation of natural moisturizing factor.

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To better understand these functions, it is important to understand the structure of the stratum corneum, including how the skin barrier functions. The scientific community has likened the stratum corneum structure to a “brick and mortar” wall. This is a common description that most estheticians know, but it is more complicated than this simplified analogy.

Corneocyte 'Bricks'

In this analogy, bricks refer to corneocytes. These are the “dead” cells we usually exfoliate and generally try to hydrate. These cells no longer have a nucleus and are incapable of molecular synthesis, but they are filled with bundles of keratin proteins essential to maintaining the mechanical integrity of skin.

Included within corneocytes is another protein called filaggrin. This protein is digested by enzymes called proteases, which produces smaller molecules that become the skin's natural moisturizing factor (NMF). NMF is essential to the health of the skin's barrier because it attracts and binds water.

There are more than 20 different proteins surrounding the corneocyte, essentially cross-linking together through chemical connections. Think of it similar to a split-rail fence surrounding a yard—the barrier is porous and rigid, and its purpose is to resist the mechanical stress imposed upon skin on a daily basis.

Lipid 'Mortar'

The mortar in this analogy refers to lipids, also known as lamellar membranes, which surround the corneocyte. These are produced by epidermal cells and stored within keratinocytes in entities known as lamellar bodies. As keratinocytes move up into the stratum corneum, these lamellar bodies are secreted into the extracellular matrix surrounding the corneocyte. The lipids secreted are organized into sheets called lamellar membranes.

A healthy lamellar membrane will have lipids in the correct 1:1:1 ratio of sterols (cholesterol) to ceramides to free fatty acids. This ratio must be maintained for a healthy permeability barrier, which is essential to prevent water loss and foreign molecules such as allergens, free radicals, toxins and microorganisms from entering the skin.

Although it contains "dead" corneocytes, the stratum corneum is metabolically active. It uses enzymes and signaling molecules called cytokines to direct the epidermis to desquamate (shed), reduce inflammation, increase lipid production and create more cells.

The surface of the stratum corneum is the acid mantle. When the pH of the acid mantle is altered from its naturally acidic state, signaling processes activate the skin’s natural healing process. However, chronic damage to the acid mantle will result in chronic inflammation, and reduced UVB protection and water-holding capabilities.

Why Corneobiology?

An esthetician’s primary work is performed on the stratum corneum through a variety of modalities, so understanding these structures and functions is essential to avoid harming the skin as well as positively influencing skin health. When one or more barrier functions is impaired, the entire system is compromised; this is the basis for a holistic approach to skin care.

Katheryn Mazierski, corneotherapy expert, esthetician and U.S. distributor of Dermaviduals skin care states, “Today, corneotherapy can be best described as an approach to the treatment and prevention of a variety of skin disorders and conditions by focusing on the repair and correction of the skin's barrier function." This is accomplished by specifically targeting the stratum corneum.

She adds, "Corneotherapy is not a quick fix ... depending on the severity of damage, genetics, age and other factors, several cellular cycles must take place in order to remove diseased tissue and replace it with healthy and functional barrier components. Estheticians practicing corneotherapy must be honest with their clients about how much time it takes but there are ways in the treatment plan to show improvement along the road to correction.”

According to Mazierski, the fundamentals of effective corneotherapy include the following.

Respect the integrity of the epidermis, starting with the first lines of barrier defense.

Keep the skin’s surface pH acidic.

Restore the antimicrobial barrier and natural UVB filters.

Use only barrier repair products that provide ceramides, cholesterol and free fatty acids in a 1:1:1 or 3:1:1 ratio.

Corneotherapy in the Treatment Room

Understanding the fundamentals of corneotherapy is one thing, but the skin care professional must translate those fundamentals to the treatment room. This starts with the ability to identify a client who has an impaired barrier.

An important piece of the puzzle is the client’s health history. Pay particular attention to inflammatory conditions such as asthma, allergic rhinitis (allergies), arthritis, atopic dermatitis, heart disease, cancer, rosacea, seborrheic dermatitis, lupus, diabetes or other autoimmune diseases. Also know that chronic inflammatory processes will impact the skin, so it will be important to follow the principles of corneotherapy in order to avoid causing additional damage. Such therapies should include the following.

Skin care. Maintaining the correct pH of the acid mantle is essential to repairing and preventing a disrupted skin barrier. Also, a barrier repair cream should have the correct key species of lipids in a molar ratio of 1:1:1. Note that emulsifiers in formulations can disrupt the skin’s barrier and cause allergic reactions.

Furthermore, although each barrier protection cream is different, many occlude the skin to stop trans-epidermal water loss (TEWL). It is important to know that such occlusion can disrupt the stratum corneum function and repair.

Cleansers should respect the skin and omit highly alkalizing cleansers such as soap. In addition, skin care products that avoid artificial fragrance, preservatives, colorants, mineral oils and other petroleum-based products are recommended.

Exfoliation. Use caution when performing exfoliation treatments. Treatments such as dermaplaning and chemicals peels in particular may need to be avoided on those with a compromised barrier and those with healthy skin will require pretreatment to ensure an intact permeability barrier.

Stimulating modalities. Take caution when performing modalities designed to stimulate epidermal cells or promote an inflammation cascade. Microneedling, microcurrent, LED, laser/IPL and radio frequency in particular may need to be avoided in clients who have a compromised barrier. For others whose barrier has been repaired, these treatments may be appropriate; still others may never be good candidates for these treatments, based on their skin's impairment.

An Evolving Science

As a body of science, corneobiology and corneotherapy are evolving. The principles of this highly studied approach are clear, while the application within the professional skin field is yet advancing. Such treatments are not based on a specific manufacturer or device, and much misinformation about the definition of corneotherapy is out there. To truly understand this approach, obtain additional education to gain a deeper understanding of the biology of skin as well as how to perform corneotherapy treatments.

Susanne Schmaling is a NCEA certified, licensed master esthetician, laser technician and accomplished instructor. With over 21 years of experience, her career has encompassed all aspects of the spa world including sales, spa ownership and medical spa modalities. She is part of Skin Inc. magazine’s advisory board and created ASCP’s Skinpro online education series (2012). She is also an esthetic book author.